The primary objective of this proposal is to determine if microRNAs participate in the regulation of critical genes implicated in lung cancer drug sensitivity. We have developed a computational method to predict interactions between miRNAs and mRNAs. Based on this method, we predict that a number of oncogenes, tumor suppressor genes, and genes relevant to drug resistance are regulated by miRNAs. We have confirmed several of these predictions using miRNA expression profiling data on a small number of cell lines, including small cell lung cancer (SCLC), non-small cell lung cancer (NSCLC) and immortalized human bronchial epithelial (HBEC) cell lines. We will use a combination of in silico and in vitro approaches to address the following questions: Are specific microRNA expression profiles correlated with differential drug sensitivity in lung cancer cell lines? Do microRNAs play a functional role in drug sensitivity/resistance of lung cancer cells? Can microRNA expression levels be manipulated to increase drug sensitivity of lung cancer cells in cell culture? Study design: We will use microRNA microarray to identify miRNAs that are differentially expressed across a panel of lung cancer cell lines. We will then predict the mRNA targets of the regulated miRNAs using both our own bioinformatics tools as well as those developed by other investigators. We will perform studies in cultured cells using a reporter assay system to determine if expression of the miRNA is associated with repressed translation of the predicted target mRNA in cultured cells. Finally, we will determine if over-expression or silencing of the microRNAs affects mRNA translation of the target gene(s) and results in specific changes in sensitivity to widely-used anti-cancer drugs. Cancer relevance: Identifying aberrant miRNA expression consistent with the models of miRNA involvement in cancer can provide new insight into lung cancer disease mechanisms, and a new set of diagnostic markers and therapeutic targets which could play a significant role in the treatment of human disease.